The fronts of your teeth shaped and polished about a fingernail's width on the front of your teeth to make room for a nice fitting covering. An impression is taken and sent to a lab, and you wear some temporary veneers while the lab makes them. When you return the temporary veneers and taken off and the permanent veneers the lab made are then bonded on and virtually look like and are a part of your teeth.
If the gap between your front teeth is significantly large, then placing a bonding material to close that gap may make your two front teeth look abnormally large. A better option for immediate results would be to place porcelain restorations, most likely involving more teeth so they look proportionally sized and line up properly. This would give you a more predictable outcome and better overall appearance. Orthodontics can be a viable alternative if you like the shape and shade of your teeth. You would not have to reduce the teeth or add any bulking bonded restorations, and you can improve the alignment of your teeth significantly. Talk to your dentist to see what options are best for you.
The aligners involved with Invisalign treatment can produce result that close gaps and retract front teeth to make them align with the rest of your upper teeth better. The alternative would be to have tooth colored brackets placed on your teeth, which can also give results you desire. Seek a consultation by a dental professional proficient in orthodontics to determine which option is best for you.
At one time it was pretty routine to take out certain teeth before orthodontic treatment to create space, but that practice is now diminishing. Long term adverse effects, such as the arches of the jaws collapsing, were becoming more frequent, so many dentist now choose to extract only if completely necessary. If you are unsure of the treatment proposed to you, seek out another opinion to help you make this important decision.
The most common side effects to teeth whitening is sensitivity, usually to cold. Other times patients can experience a throbbing sensation to whitening. There are products that can be used during treatment to help decrease these effects, along with medication. The degree of severity of these side effects can differ from person to person, however, and it is difficult to eliminate them completely. Many times beauty has a price, but hopefully in the end your smile is improved and you will feel it was worth it!